1. Field of the Invention
This invention relates to means for mounting a ring laser gyroscope or other precision inertial or optical instrument, and particularly to a means for mounting such a precision instrument to minimize the transmission of detrimental stresses to dimensionally critical parts of the instrument.
2. Description of the Prior Art
Some of the prior art techniques for mounting precision instruments, such as ring laser gyroscopes, utilize metallic attachments by hard surface mounting, hard point mounting or spring mounting. Each of these techniques suffers from the disadvantages of transmitting stresses which can cause a distortion of the critical ring laser gyroscope structure and/or does not provide sufficient support for higher acceleration or vibration environments. A detrimental distortion of the ring laser gyroscope structure can arise from mechanical stresses in the mount attachment itself, as well as from external thermal, accelerational or vibrational effects transmitted through the mounting structure. Experience has shown that whenever a ring laser gyroscope structure is hard mounted, there is sufficient distortion of the structure to degrade performance. In a hard-mounted structure mounting stresses, and hence performance, can also vary with environmental changes. Whenever a ring laser gyroscope, or other precision instrument, is mounted for operation by the use of a metallic spring mounting, stresses are not transmitted so readily. However, the metallic spring mounting is less able than one of the hard-mounted techniques to resist acceleration or vibrational inputs and tends to be sensitive to spatial orientation.
In using any of the above-described prior art mounting techniques even a very small dimensional change in one of the critical parts of a mounted precision instrument can adversely affect the instrument. A ring laser gyroscope, for example, is sensitive to very small changes in the relative positions of the mirrors which define the ring laser gyroscope optical cavity. To degrade gyroscope performance, the mirror positions need to change only enough to move the laser beam position a small fraction of a wavelength. Since the operational wavelength of the helium-neon laser in a typical ring laser gyroscope is approximately 25 microinches, a dimensional distortion of only a few microinches is detrimental. Thus, if the dimensionally critical structure of a ring laser gyroscope is compressed or stretched unsymmetrically by several microinches or warped or twisted through about one arcsecond, the points of incidence of the laser beams on the mirrors will be sufficiently shifted to degrade the operational performance of the ring laser gyroscope.